The proposed study is designed to answer the following questions: (1) What does a rodent do with its incisors?; (2) Are there different types of incisal biting?; (3) If there are different types, are these types correlated with differences in the anatomy of the masticatory apparatus?; and, (4) Are there mechanical explanations for the correlations? To answer these questions a three-part program is proposed, which includes anatomical dissections, mechanical analyses, and observations in vivo which will include EMG and video-flouroscopy. Two species have been selected that present different combinations of incisal morphology and masticatory muscles. When the research is completed, I will have some knowledge of the components of the masticatory apparatus of each species, how each system works, and what each animal does with what it has. By comparing the two species, I hope to find inter-specific differences in the use of the incisors that are the results of mechanical differences between the masticatory systems of the four species. Such correlates can be used in future studies to predict the biting behaviors of rodents from the morphology of their masticatory apparatus.